1. Field of the Invention
The present invention relates to an exposure control apparatus based on the known multimetering system according which an object field is divided into a plural number of areas and the areas are photometrically measured individually.
2. DESCRIPTION OF THE PRIOR ART
When one takes a picture under backlight conditions using a conventional camera, it is required to suitably correct the exposure value automatically determined. According to the prior art this correction is made relying solely on the photographer's experience with the ASA sensitivity correction dial or a particularly provided correction switch. In the former case, considering the state of the backlighted object, the dial is reset toward overexposure by one or two steps. In the latter case, by turning the correction switch, the exposure value is corrected to a predetermined value which corresponds to one and half step overexposure. It is true that these correction methods have some effects for obtaining good pictures. However, the result obtainable from such correction varies case by case according to the state of the object at that time. To obtain consistently good results from such correction, a high degree of experience and skill is required. The same may be said of the case in which the correction has to be made toward underexposure, for instance, to take a picture of such scene including a spotlighted object.
Some attempts have already been made to automatically determine the correction of exposure necessary for the above mentioned cases without relying on the photographer's experience and skillfulness. A potential solution to the problem is to use a plural number of photo receptors as proposed by U.S. Pat. No. 4,214,826 (the counterpart of which is DAS No. 2,632,893) and U.S. Ser. No. 123,209 (the counterpart of which is DOS No. 3,007,575).
According to the known solution, a multiple light measurement of a scene to be taken is carried out using a plural number of photoelectric elements. From the photometric outputs of the multiple metering there are obtained by calculation about three different reference outputs (the maximum photometric output Pmax, the mean photometric output Pmean and the minimum photometric output Pmin). One of the three reference outputs is selected based on the result of classification of the object into one of the predetermined categories. This method is more effective to correct the exposure value than the conventional correcting method relying on the photographer's experience and skill. However, this correcting method employing a multimetering skill involves some problems. For some objects there occurs erroneous classification of the object which results in misselection of the reference output. Furthermore, when the main object is smaller than one divisional area of the divided object field, it is impossible to obtain any correct information of brightness. For example, this is applied to the case where the object to be taken is a single flower standing against the white background. In this case, all of the measured outputs will have the same value which corresponds to the brightness of the white background only. The camera, therefore, perceives the scene merely as a flat object. In this case, almost the same exposure value is automatically set whichever the apparatus may select from the three reference outputs, Pmax, Pmean and Pmin. In any case, the result is underexposure. This erroneous exposure may be corrected to some extent by additionally using manual film sensitivity changing means such as the above mentioned ASA correction dial. However, in such case, when the difference in brightness between the areas becomes large, a doubled correction may be made by the manual dial correction on one side and by the automatic correcting function of the camera itself on the other hand. Such doubled correction will lead to overexposure which is entirely opposite to that as given by automatic correction only.